1. Field of the Invention
The present invention relates to a resistance dividing circuit for generating gray-scale voltages.
2. Description of Related Art
There are widely used display devices, such as a TFT (Thin Film Transistor) liquid crystal display device, a simple matrix type liquid crystal display device, an electroluminescence (EL) display device, a plasma display device, and the like.
In such a display device, for controlling the gray-scale level of a pixel, a gray-scale voltage generating circuit is used which generates a gray-scale voltage to be applied to the pixel. FIG. 1 shows a portion of such a circuit. On a substrate, a resistive element 155 is provided which extends in a predetermined extending direction. Between a first end (not shown) and a second end (not shown) of the resistive element 155, a reference voltage is applied. At a plurality of tap connection sections 160 set to place between the first and second ends of the resistive element 155, projecting sections 153-2 are respectively formed with electric conducting material. At each projecting section 153-2, a contact 153-1 is formed. The projecting section 153-2 and the contact 153-1 form a tap 153. A voltage between the plurality of taps 153 is extracted from the potentials supplied by the plurality of contacts 153-1 for generating a gray-scale voltage.
In Japanese Laid-Open Patent Application (JP-P2003-152079A), a method for designing a reference voltage generation system is described. In this method, in the middle of a resistive element which is electrically uniform across the entire lengthwise region across which a constant voltage is fed, voltage extraction sections generating voltages of mutually different values are arranged based on correlation between resistance values of these voltage extraction sections in accordance with values of voltage to be generated. This designing method is characterized in that: a bending portion whose resistance value is previously measured is formed between the aforementioned voltage extraction sections in the resistive element in accordance with an area of a region on a semiconductor integrated circuit where the resistive element needs to be arranged; a correlation coefficient for converting a length of a current path at the bending portion calculated by using an actually measured resistance value of the bending portion into a length of the linear portion of this current path is calculated; and a value of resistance between the voltage extraction sections including the bending portion is obtained by using this correction coefficient. This consequently permits achieving space saving with a simple configuration and also providing a reference voltage with high accuracy for each gray-scale.